Cognitive dysfunction in the aging Veteran population is a growing health concern in the Veterans Health System. While neurodegenerative disorders, like Alzheimer's disease, Parkinson's disease and Multiple Sclerosis have received considerable attention as potential etiologies for dementia, obstructive sleep apnea (OSA), that also produces significant neurocognitive sequelae remains unrecognized as a cause. This is surprising given that the prevalence of sleep apnea in elderly Veterans has been estimated to be up to 40%. Moreover, chronic lung disease, particularly COPD, is now also thought to contribute to cognitive decline possibly through hypoxic injury to the brain. However, it is not known whether OSA coexisting with COPD will enhance the risk for cognitive dysfunction. Thus, we sought to investigate whether these two highly prevalent diseases, that often co-exist as the 'Overlap Syndrome', combine to enhance cognitive impairment in the elderly Veteran population. Additionally, treatment of OSA with positive airway pressure (PAP) has been shown to improve neurocognitive function in moderate-to-severe OSA while cognitive decline in COPD may be reversible through treatment with long-term oxygen therapy. Thus, it is conceivable that developing treatment strategies that target the pathophysiological underpinnings of the Overlap Syndrome, aimed at repairing hypoxia and arousal-induced 'brain injury', will allow recovery of neurocognitive function. Specific Aim 1 will investigate whether elderly Veterans with the Overlap Syndrome have increased neurocognitive deficits compared with OSA or COPD alone. Specific Aim 2 will further study the Overlap Syndrome group to determine whether treatment with CPAP and supplemental oxygen vs. CPAP alone will improve neurocognitive function and reduce sleepiness in conjunction with improved quality of life. Thus, using a novel dual-pronged strategy we hope to eventually delay the onset of dementia in a high-risk Veteran population. This pilot project will allow us to determine feasibility and sample size for a future larger long-term trial. Ultimately, our goal is to enhance rehabilitation and recovery from injury caused by two chronic conditions and thus, improve the overall health and quality of life of elderly Veterans.